Twenty-nine RCTs were included (n=1,794 participants): 22 parallel-group designs (n=1,296 participants) and seven crossover designs (n=498 participants). Twenty-five studies had a Jadad score of 3 points or more and were considered high quality. Twenty-seven studies had proper allocation concealment. Trial duration ranged from two to 26 weeks.
Garlic in comparison with placebo was associated with a reduction in levels of total cholesterol (WMD -0.19 mmol/L 95% CI -0.33 to - 0.06; I2=64.3%; 28 RCTs), triacylglycerol (WMD -0.11mmol/L, 95% CI - 0.19 to -0.03; I2=26.7%; 28 RCTs), low-density lipoprotein (WMD - 0.059mmol/L, 95% CI -0.151 to 0.032; I2=24%), and high-density lipoprotein (WMD 0.025mmol/L, 95% CI -0.001 to 0.051; I2=9.6%). No evidence of publication bias was found.
Sub-group analyses suggested that there were no statistically significant differences in the effects of garlic on total cholesterol, low-density lipoprotein, high-density lipoprotein and triacylglycerol with respect to trial quality, trial duration, type/brand of garlic, baseline total cholesterol, baseline triacylglycerol and diet control.